1. Field of the Invention
This invention relates to wells, especially wells such as oil wells which are produced through use of gas injected into the well at the surface to aid in lifting oil and/or other liquids to the surface, and particularly relates to valves for controlling the admission of such gas into the oil and/or other liquids at a subsurface location.
2. Related Art and Information
Gas lift valves have been used for many years to aid in the production of oil wells lacking sufficient natural pressure to flow naturally without assistance. Such valves commonly control the admission of lift gas into the well tubing from the well casing to aid in lifting formation liquids to the surface. Lift gas is generally injected into the well casing at the surface. Several types of gas lift valves have been known. Some gas lift valves open in response to casing pressure, some in response to tubing pressure, some admit gas into the tubing continuously, other under certain conditions. Some gas lift valves, for instance, are provided with main valves which are pilot actuated, that is, when their pilot valves open, their main valves are caused to open, and when their pilot valves close, their main valves close in response thereto. The pilot valve may respond to casing pressure or to tubing pressure or to the difference between those two pressures.
Listed here are certain U.S. patents which disclose prior gas lift valves which may be pertinent to the invention disclosed and claimed in this present application.
Re. No. 25,292 2,385,316 2,642,811 2,642,812 PA0 2,994,335 3,086,593 3,105,509 3,125,113 PA0 3,143,128 3,183,922 3,311,126 3,311,127 PA0 3,326,229 3,386,391
U.S. Pat. No. 2,385,316 which issued on Sept. 18, 1945 to Robert 0. Walton discloses a gas lift valve having a main valve 29 for controlling flow of lift gas into the tubing from the casing. Main valve 29 has a bellows 30 the interior of which is exposed to casing pressure through passage 32. Pilot valve 38 normally prevents casing pressure from bellows 30 from bleeding off into the tubing. Pilot valve 38 is pressed by spring 48 toward closed position. A second bellows 44 attached to the pilot valve is exposed to tubing pressure. When tubing pressure rises to a predetermined level, the bellows 44 overcomes the force of spring 48 and unseats pilot valve 38. This causes casing pressure to bleed from bellows 30 of the main valve faster than small passage 32 can replenish the casing pressure and the main valve opens. Pilot bellows 44 is almost filled with an incompressible liquid which permits limited compression of the bellows and which protects it from damage (crushing) by excessive pressure.
U.S. Pat. No. 2,642,811 issued to C. D. Fletcher on June 23, 1953. This patent discloses a well flow apparatus and system, the heart of which is a gas lift valve. This gas lift valve is pilot operated. The pilot valve 25 has a spring 27 normally holding it in closed position. It also has a bellows 23 which is exposed to casing pressure. When the casing pressure rises to a sufficiently high level, the bellows 23 is compressed, overcoming the force of spring 27 and unseating pilot valve 25. This allows casing pressure into bore 30 and to act upon the exterior of bellows 32 to compress the same and open the main valve 38 to permit lift gas to flow from the casing into the tubing through passage 41. When casing pressure is reduced sufficiently, the pilot valve will no longer be held open thereby and will close. This ex-communicates the bellows 32 from casing pressure and the casing pressure exterior of this bellows will soon bleed through port 37 of the bellows sufficiently to cause the main valve to close. This gas lift valve has the pilot bellows almost filled with liquid to permit limited compression of the bellows but also protect the bellows from being damaged by overpressuring.
U.S. Pat. No. 2,642,812 issued to A. I. Robinson on June 23, 1953. This patent is a well flow apparatus which utilizes two gas lift valves of the pilot operated type. The first valve (FIG. 2) is of virtually the same structure as that disclosed in U.S. Pat. No. 2,642,811 just discussed and operates in the same manner to transfer lift gas from the casing into the tubing. The pilot of gas lift valve D1 of FIG. 2 has its pilot bellows exposed to casing pressure. The device El of FIG. 4 of U.S. Pat. No. 2,642,812 is the same structure as the valve D1 but transfers lift gas outwardly from an input conduit to an outer conduit. This is commonly done, but generally lift gas is transferred from an annulus inwardly into the tubing. Again, liquid is used in the pilot bellows to protect it from crushing under excessive pressures. Both such valves are used in a plural well where an annulus is used for supplying lift gas to both valves, one of which transfers gas into the tubing and the other of which transfers gas into an outer annulus.
U.S. Pat. No. 2,994,335 issued to W. A. Dudley on Aug. 1, 1961 and its reissue Patent Re. No. 25,292 issued on Dec. 4, 1962, disclose a gas lift valve which has a pilot valve with a bellows and spring, the spring for biasing the pilot valve toward closed position and the bellows, exposed to casing pressure for moving the pilot valve toward open position. When casing pressure rises to a predetermined value the bellows lifts the pilot valve to open position in opposition to the spring. When the pilot valve opens casing pressure enters through the pilot valve to act upon the main valve and move it to open position against the force of its spring to allow transfer of lift gas into the tubing. When the casing pressure falls below a predetermined value the pilot valve will close and this will result in the main valve closing, it being moved by its spring.
U.S. Pat. No. 3,086,593 which issued on Apr. 29, 1963 to C. B. Chitwood discloses a gas lift valve having a pilot valve including a bellows attached to the pilot valve member and charged with a compressed gas. The bellows hold the pilot valve on its seat (closed) when the casing pressure to which it is exposed is below a predetermined level. When the casing pressure rises above such predetermined level, the bellows will be compressed and will unseat (open) the pilot valve. Opening the pilot valve allows casing pressure to move the main valve to open position against the compression of its spring. When casing pressure falls below the predetermined level, the pilot valve closes, whereupon the main valve is returned to closed position by the spring.
U.S. Pat. No. 3,105,509 issued Oct. 1, 1963 to H. H. Moore, Jr. and discloses a gas lift valve for chamber lift operations. The valve is pilot operated. It has a pilot mechanism which includes a pilot valve 35 movable between closed and open positions by a bellows 37 attached thereto. The bellows is charged with pressurized gas. The bellows is exposed to casing pressure at all times. When casing pressure rises to a predetermined level it compresses the bellows and opens the pilot valve. This allows casing pressure to move the main valve 27 to open position against the force of spring 30. When the pilot valve closes, the main valve will quickly close. The bellows is charged with a pressurized gas.
U.S. Pat. No. 3,143,128 issued to Lewis J. Bicking on Aug. 4, 1964. This patent discloses a pilot operated valve. Pilot valve 45 is held on seat 44 by spring 48. Casing pressure admitted through port 38 and vertical passage 39 occupies the spring chamber when the pilot valve is seated. Casing pressure is also allowed to enter port 55 and surround the bellows 46. When casing pressure rises above a predetermined pressure, bellows 46 attached to pilot valve 45 will compress and unseat the same and pressure in the spring chamber will bleed through seat 44 faster than it can enter through port 38 and passage 39. This decreases the pressure above piston 36 from which main valve 33 is depended. Casing pressure, communicated through ports 25 will readily lift the main valve to full open position to allow fluid flow through ports 25, bore 27, and exit ports 28 into the tubing. The contents of the bellows is not found to be specified.
U.S. Pat. No. 3,183,922 which issued May 18, 1985 to C. P. Lamb, et al., discloses a pilot operated gas lift valve. The pilot valve (ball 72) is held on seat 71 by pilot spring 74 and bellows 63. The bellows is exposed to tubing pressure conducted thereto through outlet 21, main valve stem bore 34, and passage 62. Casing pressure is communicated to the ball and seat via passage 59. When casing pressure increases to a predetermined value, ball 72 will be unseated and casing pressure flowing through the seat will pass through passage 62 and will be applied to piston 35 to thus move it down in opposition to main valve spring 44. Main valve 48 attached to the piston will thus be unseated and moved to its open position. When the casing pressure falls to a predetermined value, the pilot spring and the bellows will return the ball 72 to its seat to bar further entry of casing pressure. This will allow tubing pressure to equalize on upper and lower sides of the piston and permit spring 44 to close the main valve. It is not stated that the bellows contains anything.
U.S. Pat. No. 3,311,126 which issued to William A. Dudley on Mar. 28, 1967 and discloses a pilot operated gas lift valve. This device has a pilot valve 60 which engages seat 70. Pilot spring 75 biases the pilot valve towards its seat. A bellows 72 is also connected to the pilot valve. Port 69 communicates casing pressure into the pilot valve chamber. When casing pressure reaches a selected level, the bellows 72 compresses, overcomes spring 75, and lifts pilot valve 68 off its seat. Casing pressure then flows through seat 70 and its passage 71 into the chamber (47) therebelow where it acts upon piston (18). The piston is thus depressed, compressing spring 55 and opening the main valve 17 to permit flow of lift gas from the casing into the tubing through inlet screen 38, inlet ports 37 and through bores 42 and 43, to exit through outlet ports 39. When the casing pressure falls below the selected level, pilot valve 68 closes, chamber (47) is shut off from the casing pressure and becomes equalized with tubing pressure, the excess pressure bleeding to the tubing through bore 64 of the piston (18) and its stem 17. With pressures equalized above and below the piston, main valve spring 55 moves the main valve to closed position.
U.S. Pat. No. 3,311,127 issued on Mar. 28, 1967 to William A. Dudley. This patent discloses pilot operated gas lift valve wherein unseating of the trigger valve 31, FIG. 3, results in the opening of the pilot valve 42 and of the main valve 23 for a selected period to permit flow of fluids from the inlet 19 to the outlet 21. To maintain the main valve 23 open for this selected time, an incompressible liquid, contained between a spring pressed lower pressure responsive member 35 and a spring pressed upper pressure responsive member 53 is metered through passages in the partition 48 between them. The rate of flow through these passages is adjusted by needle valves. When the trigger valve 31 is seated again, the main valve 23 will close.
U.S. Pat. No. 3,326,229 which issued on June 20, 1967 also to William A. Dudley discloses a gas lift valve which appears to be the same as that illustrated and described in his just mentioned Pat. No. 3,311,127.
U.S. Pat. No. 3,386,391 which issued to Henry U. Garrett on June 4, 1968 discloses a gas lift valve and systems and methods for unloading wells equipped therewith. The gas lift valves disclosed and claimed are not pilot operated valves, they open in response to tubing pressure and close in response to casing pressure, they are provided with means for latching the valve member in its open position automatically upon its reaching full open position. The latching means is releasable responsive to a decrease in casing pressure to a predetermined low value, whereupon the valve members move to closed position and afterwards will not open in response to casing pressure. The methods are described as unloading a well automatically and needs no attention or clock controls as it will completely unload and come back to operating pressure for either testing or normal operation if desired.
There was not found in the known prior art a pilot operated gas lift valve having therein a body of compressible liquid therein and an associated mechanism including means sensitive to such liquid's volumetric changes due to changes in pressures acting thereon for actuating the pilot valve to control opening and closing of the main valve. Neither was there found any system utilizing such gas lift valves, nor any method for unloading and operating a well equipped with such gas lift valves and system.
The present invention is an improvement over known gas lift valves of the unloading type, as well as known systems and methods relating thereto.